Clamp devices, including pliers-type tools or wrenches, have been in use for a long time. Such tools typically have a pair of opposed jaws defining a workpiece receiving space. At least one of the jaws is movable with respect to the other, and a handle usually is associated with each jaw. The jaws may be connected pivotally so that when the handles are moved inwardly or outwardly with respect to each other, the jaws will be caused to move similarly. U.S. Pat. No. 597,740 discloses such a pliers and that it is known to provide a pliers with jaws that remain parallel as the pliers is operated. U.S. Pat. No. 682,701 discloses another pliers with a central pivot and parallel locking jaws.
U.S. Pat. No. 120,144 discloses an improved pincher or pliers that includes a lever having a cam-like projection at one edge. The projection is shaped so that when the lever and an opposing arm, which together form the handles of the pincher, press together, it raises the rear end and depresses the front end of one of the jaws, closing the jaws together.
None of the above-noted patents discloses an adjustment feature associated with the jaws, other than simple handle movement, to vary the compressive force exerted by the jaws on a gripped object. There are commercially available pliers wherein the space between the jaws may be varied, but the adjustment involves shifting an entire jaw/handle unit about a central pivot or operating a screw device connected to one of the handles. It would be advantageous to be able to vary the compressive force exerted by the jaws conveniently and rapidly prior to manipulating the handles and without resorting to additional lever or screw features associated with the handles.
U.S. Pat. Nos. 2,825,525, 4,077,601 and 798,827 disclose that pliers-type tools have been adapted for use as hose clamps or compressors. For example, U.S. Pat. No. 798,827 discloses a jaw member pivoted to a main lever, brackets on either side of the jaw, and a cam lever arrangement. The closing of the jaw member is accomplished by swinging the cam lever downwardly, causing a cam loop to press against a bearing plate, forcing the jaw member to swing toward the main lever. The jaw member and main lever are rounded to prevent cutting the hose to be clamped. The hose clamp disclosed in U.S. Pat. No. 4,582,292 is somewhat similar and is directed to reducing the chance that the hose will pop out from between the jaws when the jaws are opened.
U.S. Pat. No. 3,460,797 discloses a hose compressor including a clamping arm hingedly connected to one end of a base. Two toggle arms extend upwardly on opposite sides of the clamping arm and are connected to a handle. Forward movement of the handle moves the toggle arms forward to open the clamping jaws. The jaws include opposing jaw faces with recesses for receiving narrow, elongated jaw inserts with curved surfaces. The inserts are formed from elastomeric material.
While the above-cited patents and commercially available pliers show improvements and advances in clamping tools, and in adapting such tools for compressing a conduit to control the flow of material in the conduit, there are some inadequately addressed problems. First, while any jaw-type clamp defines a workpiece receiving space between its jaws, the only way to vary that space, and the compressive pressure exerted by the jaws on a workpiece, is to manipulate the handles or screw or lever structures associated directly with the handles. It would be advantageous if the space remaining between the jaws, when the jaws are closed fully, could be selected easily, rapidly and precisely prior to placing the tool on a conduit and prior to applying compressive force to the conduit. When clamping relatively soft-walled conduits, particularly those conveying potentially hazardous or flammable material, it is crucial that the jaws be adjusted appropriately prior to exerting a compressive force, thereby minimizing the chance of damaging the conduit, yet ensuring that the lumen of the conduit is completely closed.
Another problem is that a clamp tool may need to be left in place on a conduit for an indeterminate length of time. Thus, it would be advantageous to be able to set a tool on a conduit and release the handles, yet have the tool remain in place as long as necessary without resorting to complicated locking mechanisms. To prevent tampering or when the clamp must remain in place for an extended time, it would be an advantage if the clamp had a simple auxiliary lock receiving feature for receiving a pin, bolt or padlock, thereby rendering the handles unmovable.
Still another problem is that prior art clamps generally are designed to grip an object from the side, not from directly above the object. It would be helpful if a clamp could be applied from above a conduit with confidence that it would entirely compress the conduit and remain in place. This would be particularly helpful when the conduit is in a confined area such as a narrow trench.
Additional concerns include providing a clamp that may be grasped and operated securely by a user in adverse conditions such as freezing or wet weather. The weight of the clamp should be light so that it may be carried easily to worksites or to remote locations. It should be durable and fabricated of a spark resistant material.
Clearly, there is a need for an efficient, durable conduit clamp that completely controls the flow in a conduit, minimizes problems with handling, maximizes safety, and may be adjusted accurately, easily and quickly for use on conduits of different sizes.